JPS581191B2 - Denkaiyo Asbestos Kakumakuno Seizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an asbestos diaphragm for electrolysis that is strong and has excellent water permeability.

More specifically, the present invention relates to a method for manufacturing an asbestos diaphragm containing polymer pulp strongly bonded with alkali.

Conventionally, asbestos diaphragms are the only type of electrolytic diaphragm used, but as is well known, asbestos diaphragms have weak bonds between asbestos fibers, and chrysotile asbestos, which is its main ingredient, lacks acid resistance. There is a problem that it lacks durability.

Therefore, various developments have been made, such as using polymers as a binding material between asbestos fibers and creating an electrolytic diaphragm made of polymers alone using a network of polymer fibers.

However, when ordinary polymers are used, gas is easily adsorbed on the polymer surface because the polymer is hydrophobic, resulting in a significant decrease in water permeability and an increase in voltage. I haven't been able to do it.

Therefore, if a membrane can be made that is hydrophilic and has the same strength as when using a polymer, it is highly conceivable that it will be an excellent diaphragm.

A commonly used method for this purpose is to treat asbestos fibers with an aqueous solution containing an inorganic substance, such as caustic alkali, and dry them, thereby solidifying asbestos fibers with caustic alkali.

Membranes made using this method of using inorganic substances as binders are good because they are made only of hydrophilic surfaces and have no adverse effects such as gas adsorption and are strong. When the asbestos fibers come in contact with and then harden by drying, they harden tightly between the asbestos fibers, filling the pores that allow water to pass through, and even if they do not fill the pores, the pores formed by the asbestos fibers become extremely small. Therefore, it is easy to form a membrane with low water permeability, and when electrolysis is actually performed,
The head of the anode chamber becomes very high, which can be a problem.

The present inventors have found that after forming a film from asbestos fibers and polymer pulp dispersed in water, heat-treating it at a temperature higher than the separation point of the polymer pulp, and then drying it after treatment with an aqueous solution containing caustic soda, an extremely excellent electrolysis effect can be achieved. discovered that a diaphragm could be obtained,
A patent application was filed.

[Unexamined Japanese Patent Publication No. 51-107284=Patent Application No. 50-3
2152)].

According to this method, the asbestos fibers formed into a film are bonded by once melting and solidifying the mixed polymer bulk, and the asbestos is further strengthened by caustic soda treatment, making it strong and strong. A membrane with high water permeability can be obtained.

However, in this method, the process of drying and heat-treating the film formed in water takes a long time, and the process is complicated.

Furthermore, when a mixture of asbestos fibers and polymer pulp is heat-treated, the polymer pulp contracts due to the rise in temperature, and at this time, the pulp contracts while being entangled with the asbestos fibers, so relatively large voids are created around the pulp. However, increasing the amount of pulp tends to result in a membrane that exhibits non-uniform water permeability due to these voids.

As a result of extensive research into solving these problems, the inventors of the present invention have developed a method in which a film formed from asbestos fibers and polyolefin pulp dispersed in water is treated with caustic alkali without drying or heat treatment. Even the membrane obtained by drying has good water permeability, especially in this case, the asbestos in the membrane before drying is strongly bound by caustic alkali and is in a considerably clogged state. It was discovered that even when the pulp shrinks due to heat, it does not form large voids, so even if the amount of pulp increases somewhat, uneven water permeability will not be exhibited.

It has also been found that drying in this case does not necessarily have to be carried out at a temperature above the melting point of the pulp, and that even when drying is carried out below the melting point, the water permeability can be greatly improved.

Furthermore, instead of dispersing asbestos and polyolefin-in pulp in water and treating it with caustic alkali after film formation, similar results were obtained even if the asbestos and polyolefin-in pulp were dispersed in caustic alkali from the beginning and then formed into a film. Reached.

In the present invention, an asbestos film is formed by dispersing asbestos fibers and polyolefin-in pulp in water and then treating it with a caustic alkaline solution, or by dispersing asbestos fibers and polyolefin-in pulp in an aqueous solution containing caustic alkali. In a method of manufacturing an asbestos diaphragm that is firmly bonded by alkali by forming a membrane,
Freeness 50mlC. S. 5 parts by weight of polyolefin in vulp having F or more per 100 parts by weight of asbestos in the membrane.
The present invention relates to a method for manufacturing an asbestos diaphragm for electrolysis, characterized in that the asbestos diaphragm is mixed in an amount of 60 parts by weight.

To describe the present invention in more detail, the electrolytic diaphragm of the present invention is produced by dispersing and mixing asbestos fibers and polyolefin pulp in water.

The water used at this time may be, for example, a catholyte containing caustic soda, and after dispersion mixing, a film is formed by pressurization and depressurization, etc., and the temperature is 80°C.
Dry at above temperature to form a diaphragm.

Alternatively, the film may be produced by dispersing and mixing with water, forming a film, contacting with an aqueous solution containing caustic alkali, and drying in the same manner.

When forming a film, it is possible to dehydrate it on a filter cloth and create a film alone, but it is better to form the film on a cathode plate such as a porous iron plate or wire mesh because it can be incorporated into the electrolyzer as is. .

Further, the dehydration film formation may be performed by either pressurization or depressurization. For example, when forming the film directly on the cathode plate, the film may be formed by the same method as the commonly used deposit film.

The polyolefin-in pulp used here has a pulp-like branched structure made by beating a polyolefin molded product.

Because polyolefin pulp has a branched structure, it mixes well with asbestos fibers, entangles them, and forms a uniform film even though it has a hydrophobic surface.

This kind of mixing is difficult to mix with asbestos evenly when dispersed in water because polyolefin in the form of powder or thread has less entanglement with asbestos fibers, making it difficult to form a uniform mixed film. This is considered to be a characteristic of pulp-like molded products that have a structure.

Furthermore, when polyolefin pulp comes into contact with caustic alkali, it has a hydrophobic surface, so it is somewhat difficult to blend in, and when drying, it has the effect of controlling plugging with caustic alkali, shrinkage of the membrane, and helps open appropriate pores. In addition, the polyolefin-in-pulp itself shrinks due to heat, which serves to enlarge the pores created between asbestos fibers.

In addition, since polyolefin-in pulp deteriorates when exposed to chlorine gas on the anode chamber side, it has a hydrophilic property similar to that of asbestos alone, and has a structure that allows gas to escape quickly without retaining gas inside. Therefore, it has the advantage that it does not cause a decrease in water permeability or an increase in voltage due to gas retention.

The polyolefin-in-pulp used here refers to pulp made from polyethylene, polypropylene, etc., and its shape is such that the thickness of single fibers with a branched structure is 100μ or less, particularly preferably 50μ or less, and the length is 30
The thickness is preferably 5 mm or less, preferably 1 mm or more.

In particular, a freeness of 50mlC. S. F. The above is good.

The content of polyolefin pulp in the membrane is preferably in the range of 5 to 60 parts by weight per 100 parts by weight of asbestos fibers.

The caustic alkali aqueous solution here refers to 5% caustic alkali.
It refers to an aqueous solution containing from 30% by weight, and may contain various inorganic substances such as various chlorides, various hydroxides, silicates, organic substances such as surfactants, solvents, water-soluble polymers, etc. in addition to caustic alkali.

The term "caustic alkali" as used herein refers to hydroxides of alkali metals or alkaline metals such as caustic soda, caustic potash, and calcium hydroxide.

The drying temperature may be any temperature at which the caustic alkali dries, but higher temperatures are preferred because the strength of the membrane increases.

However, if the temperature is rapidly raised to over 100℃ and dried after treatment with caustic alkali, only the surface will dry rapidly, which will prevent the water inside from evaporating and cause the membrane to swell. After drying at a temperature of 100℃ or less, 100℃
It is preferable to carry out a heat treatment at a temperature of 100° C. or higher, or to gradually increase the temperature to dry the surface portion, and then further dry it at a temperature of 100° C. or higher.

As the asbestos fiber used in the present invention, one type or a mixture of two or more types of asbestos such as chrysotile, amosite, crocidolite, and tremolite are used.

As described above, the electrolytic diaphragm according to the present invention takes advantage of the characteristics of asbestos membranes, and has further strength, excellent durability, and is hydrophilic, so there is no gas retention, and there is no swelling of the membrane or water permeation. It has excellent properties, especially for electrolysis of alkali metal salts, without causing voltage drop or voltage rise.

Example 1 Chrysotile asbestos (manufactured by Johns Manville, 4T-
04) 43p and polyethylene pulp (manufactured by Mitsui Zerabak Co., Ltd., Zerabak E990, Freeness 600mlC.
S. F) After dispersing and mixing 5g in 1500cc of water,
Suction filtration was carried out using a 15 cm x 20 cm filtration device to produce a membrane-like molded product.

Next, 100 cc of a 20% aqueous solution of caustic soda was poured over the membrane-like molding, and the mixture was sucked and passed through.

After drying the formed product in a dryer at 80°C for 16 hours,
It was further dried for 2 hours in a dryer at 140°C.

Salt electrolysis was performed using the resulting membrane (sample No. 1).

The results are shown in Table 1. As a control example for sample A1, an asbestos membrane (control example 1) that did not contain polyethylene pulp and was made in the same manner was also evaluated by saline electrolysis.

The results are also shown in Table 1. The conditions for electrolysis are: Brine composition NaCl concentration 26% Mg++
, Ca++ content 10 ppm Current conditions Current density 20 A/dm2 Distance between electrodes 10 mm Anode Graphite cathode Iron-NaCl decomposition rate 50-55% Battery chamber temperature 55-60°C As can be seen from the above results, the method of the present invention using synthetic resin pulp The membrane has the excellent characteristics of low voltage and high water permeability, resulting in a low anolyte head.

Example 2 Crittile asbestos (4T-1 manufactured by Johns Manville)
2) 100 parts by weight and polyethylene pulp (manufactured by Mitsui Zerabak Co., Ltd., Zerabak E~990600ml C.S.F.
．． ) 10 parts by weight, surfactant (Pellex RP) 5
The mixture was dispersed and mixed in 6,200 parts by weight of an 18% aqueous solution of caustic soda containing parts by weight, and a film was formed under pressure on a reticulated iron cathode plate.

Next, the cathode plate was dried in a dryer at 100°C for 18 hours, and then further dried at 140°C for 2 hours.

Using the resulting cathode plate with the film as a cathode, salt was electrolyzed.

The results are shown in Table 2. Table 2 Brine composition NaCl concentration 26%Mg+
+, Ca++ content 10 ppm Current density 20 A/dm2 Electrode distance 8-meter anode Graphite cathode Iron-NaCl decomposition rate 50-55% Tank temperature 80°C Results Tank voltage 3.4 V Current efficiency 9
8% Anolyte head 110mm Current application time 30 days Example 3 Chrysotile asbestos (manufactured by Johns Manville, 4T-
04) Polypropylene fibers (manufactured by Ube Nitto Kasei, Dan Pulp Freeness 700 ml C.S.
F. ) 2g was added, stirred more vigorously, and after mixing the two well, filtered with suction using a 15cm x 20cm filtration device,
Make a film-like molded product.

Next, an 18% aqueous solution of caustic soda was passed through the membrane molded article by applying air pressure.

The resulting molded product was heated to 120° C. over 3 hours and dried for 16 hours.

Salt electrolysis was performed using the resulting film-like molded product.

The results are shown in Table 3.

Table 3 Brine composition NaCl concentration 26%Mg++
, Ca++ content 10ppm Current density 20A/dm2 Electrode distance 10mm Anode Graphite cathode Iron-NaCl decomposition rate 50-55% Tank temperature 50-60℃ Result Tank voltage 3.7■Current efficiency
98% Anolyte head 250mm Current time 100 hours

Claims (1)

[Claims] 1. By forming an asbestos film from asbestos fibers dispersed in water, treating with a caustic alkaline solution and drying, or by forming a film from asbestos fibers dispersed in a caustic alkali-containing aqueous solution and then drying. In a method for manufacturing an asbestos diaphragm firmly bonded with alkali, 50 ml of freeness C. S. F. A method for producing an asbestos diaphragm for electrolysis, comprising mixing 5 to 60 parts by weight of the above polyolefin-in-pulp with respect to 100 parts by weight of asbestos in the membrane.